Inverters for solar PV panels: your questions answered

Q1: I hear that inverters for solar PV systems typically last a maximum of 5 years, (Sunnyboy ones seem to fall over in Cambridge after a year, because of the way the grid is here). At £1,000 a pop, that makes a big difference to the economics of PV/ FITs, so it would be great to have someone blog about how to choose an inverter!.

Q2: On a solar PV system where is the best place to site the inverter? Closest to panels in a loft rather than 10/15 meters away in an attached garage? Are DC losses over the 15 meters significant to system efficiency? Do Electricity Regs cover this?

1. Inverters should last much much longer than 5 years. SMA (Sunny Boy) inverters have a 7 year warranty as standard and you can ask your installer to obtain extended warranties direct from the manufacturer if required. Like most mains connected equipment, inverters will be susceptible to mains borne transients. In rural locations this will more of an issue due to overhead power line lightning impulse pickup, etc. However, to help guard against such situations your installer will easily be able incorporate surge suppression into the PV system at minimal extra cost.

Any G83/1 compliant inverter available in the UK will be suitable, and certainly at the moment, where some smaller installers across the UK are having difficulty obtaining inverters at all, one cannot be too choosy regarding inverter type unless you are prepared for a long wait.

2. Technically, locating the inverter as close to the array to minimise DC losses is the order of the day, but in the real world other conditions prevail. In the main, inverters are large bulky items that are difficult to fit inside a standard domestic layout. For this reason they get relegated to the loft space.

This looks an ideal location, being near to the array on the roof, and in the domestic location, this will probably remain the popular choice.

There is a drawback with using the loft, it gets hot in bright sunshine which in turn will have the tendancy to prematurely overheat the inverter. Whilst the inverter can kick in its cooling fans to regulate its own temperature, the downside is it will also de-rate the output a little to minimise current throughput (and heating).

Therefore, if there is another room, large cupboard or garage that has space for the inverter, it will be better situated there. Cable losses are simply dealt with by using larger diameter cables if necessary, so no problems there.

Comments

We had a 4kW PV array installed in 2012 about 25m from the 3.6kW SunnyBoy inverter at the mains position. It has worked really well (we wonder whether it would have been even better with a 4kW inverter) but we now need to move it another 20m away from the inverter because of other building work i.e. a total of 45m. It is currently fed with 4 x 4mm cable. We have a dilema - do we:

1. extend the cabling using 4mm and see how it performs.

2. start again from new array position to inverter using a 4 x 6mm cable

The problem you have may not be heat related. On many early inverters, not just SMA Sunny Boy's were set up to disconnect from the grid at 253v.

What can now happen in the UK, all these years later, is that with the proliferation of PV being widespread, grid voltage can rise to a value much higher than 253v on a sunny summer day, causing older inverters to shut down.

I would advise you get a local electrician to pop along and plug a tester in a power socket in your house on a sunny day. If the grid voltage is over 253v, then this can be the case. Checking the display on your inverter to see the fault code at the time of the problem.

We had solar panels fitted in 2012 & have a sunny boy 3600 inverter. All was well until May this year when if we have wall to wall hot sunshine the inverter cuts out for 2 mins at a time then comes on again for 2 mins & this happens all the day until the weather cools down. The inverter is in the loft which does get hot. We are hoping to have a loft conversion so if when this is done & the loft is insulted in the roof area & the inverter is sited in an insulted area will this help the problem?

Hi, My father has an existing 10 panel system that has worked fine for 6 years. He now is planning a loft conversion and needs to reduce the system to 6 panels. He has been told that he has to have a new inverter, because the old one is designed for a 10 panel system. Is this correct, or will the existing inverter still work on a smaller system? Any advice would be greatly appreciated.Thanks

If your system is working well and is south facing with next to no shade, then changing to Solar Edge financially makes no sense, as you'll never get that money spent back.

The company who contatcted you are fibbing when they said 25% extra. Certainly a solar edge system can do 25% extra generation, but this is only when you are gettin daily shading problems only.

Also, the solar edge inverter has a 12 year warranty and the optimisers a 25 year warranty, not 30 years as suggested!.

Standard 4kW inverters such as the Zeversolar, we install for around £600 if the customer is local, so the quoted £2500 is somewhat inflated. I'd wait till the inverter goes wrong, and get it replaced then.

Incidentally, the current cost for replacing a standard system with a solar edge system is around £3000 excluding VAT. The quoted £5000 is far far too expensive. A whole 4kwp PV installation is £5000, including panels!

Sounds like this company are trying to overcharge you by a few 100 percent!

Regarding servicing and maintenance, electrical recommendations indicate they should have an inspection and test every 5 years. We charge £100 + VAt for this service. £15 a month is daylight robbery.

Hi, I am new to this forum, but was interested to see the comment from Hoppity in April about telesales companies and Solar Edge.

We had a system comprising 14 panel single string 3.5kw system with Aurora Power One invertor installed in 2013 by My Planet, who have subsequently gone out of business.

We have been very pleased with the performance of our system, but since My Planet went out of business, we have been contacted by SolarTherm (as part of a government initiative?).

They have advised that as the invertor has 5 yr warranty & we have had it for 4 years, it is likely to fail in a years time, with a typical £2,500 replacement cost. They also talk about fire risk due to evaporation of the oil (electrolyte) around the capacitors in the invertor.

Their proposed solution is to offer a Solar Edge system (1 per panel) with a new invertor, which uses Thin Film capacitors, rather than electrolytic. The new system would have a 30 year warranty, as well as providing a 25% improvement in output performance, at a cost of £5,000.

So:

1) I fully understand that equipment does not necessary fail the day after the warranty expires.

2) I consider the fire risk to be minimal as the invertor is installed in a well ventilated garage.

3) I do not know what an invertor replacement would cost.

4) I struggle to believe a 25% improvement in output as my panels are facing 10 deg off due South, with very minimal shading and are delivering the expected estimated output. An increase of 25% would mean they would be generating in excess of their rated output.

If I assume the worst case of no improved output, then the cost for the warranty is approx £15 per month for 30 years.

Should I just wait for the current Invertor to fail and then replace, or is this offer worthwhile?

There are companies out there who have somehow got their hands on a database of all PV installations in the UK, mostly including phone numbers. They are selling these databases in postcode based clusters to anyone who wants to buy them.

This means any telesales company who wants to start a business can simply invest in buying a contact list and get going on calling people to offer their service, or more likely an overpriced option you can get from your local PV installer.

This is currently covering Solar Edge upgrades, Voltage Optimisers or a service contract.. All at highly inflated prices!

However, regarding the service, the biggest offender for overpriced servicing, is ESE, who will lure you in with a 'free' service. This will turn into a £240 a year contract.. Ouch!

It is recommended that a Solar PV system is serviced every 5 years. This is to ensure that electrically it is functioning effectively and safely. Connections do get a bit loose due to heat expansion and contraction, which in turn could cause arcing and possibly a fire or burn out of the connection. However, this is a recommendation, and as an installer I offer this service for £100 for any local systems. I anticipate there are PV installers all over the UK doing the same.

Hope that helps, and as with any aspect of life DO NOT BUY ANYTHING FROM SOMEONE WHO CALLS YOU ON THE PHONE. It will ALWAYS cost you more for the service they offer than you can get elsewhere.

I have an Efergy meter displaying output from my PV system. Today, on a bright blue clear day, it's is showing a zero output. Having struggled to get into the loft, it seems the inverter is kaput. It was installed almost 6 years ago to the day so perhaps it's just gone on holiday to celebrate its birthday!

I called the service department of the manufacturer, Schuco, but they say they stopped selling solar in 2014. I've also spoken to the installer but they don't have anybody I can talk to until after the weekend.

I found the manual for the inverter and it shows a reset button. Having struggled into the loft again, the reset button produced no change at all and there are no lights on the inverter at all.

Sunny boy inverter installed in attached garage 2010 on a concrete block cavity wall supporting a 4.2 capacity system. From installation date I complained about noise level ( mains hum sound) at low generation levels i.e. From start up to around 100. This hum can be heard in bedroom above ( wall in garage goes up through bedroom,landing and hallway. Installers checked with noise level meter and from memory it was about 70db in garage at worst. They contacted manufacturers who suggested a couple of possible caused which are not applicable also a " dirty supply". They did offer to remove the inverter and take it away for testing of course no generation during this undefined period and tested by themselves so they the outcome may be to suit. In fairness the installers knowing I was not happy with outcome provided extended warranty free of charge.

I don't feel I should have to tolerate this noise level in fact if it were in the loft as usual it would be unbearable at times in all the bedrooms. Any suggestion on best way for me to proceed to resolve this. Should I first be asking the SSE to check their mains supply or buy a sound level meter to provide evidence. Thanks.

I recently learned that Inverors are required to shut down under G83 if the incoming grid voltage reaches 253v or above. have alook at the Eco Box on www.thevascogroup.co.uk more info on the box there. I had one fitted and no longer suffer from voltgae drop outs and my system is gernarating around 17% more, (based on my calcs re feed in tarrif payments) the box its a grid voltage monitor its not a voltage optimiser. hope this helps.

The main aspect to look for with any grid connect inverter is the MPPT or working voltage. I would guess that 4 standard panels would have an MPPT voltage of around 120v. You need to see if that inverter will operate at 120v in its MPPT range spec.

Also, I recall that the Sunny Roo was marketed for the Australian area, and I have seen a few going on Ebay. In addition, if you do a search, they had a habit of breaking down, similar to the early Eversolar's. Besides that, they need to be programmed to work with the UK G83/2 disconnection settings to be compliant for grid connection. It may be an option on initial start up to select from a menu.. Best check!

Otherwise, though it will operate at lower efficiancy, the 3kW inverter will work when 1kw of PV is connected. You will find it drops out sooner in low light settings than an exact matched inverter, but if your getting it cheap, thats not much to worry about!

I am looking to install 3 maybe 4 250w panels on my static caravan so output would be between 750-1000w, i have the chance of buying a sunny 3000w inverter, would it work as the output is low compared to the inverter .....any help and advice would be great....Thanks, Chris.

From the outline you have provided, the system should be OK. The things that would be critical will be the size of the cable from the array to the charge controllers. 6mm would be more than adequate, but I have seen installations with 1mm before which will severely limit the current passed.

There may be an incorrect combination of panels to charge controller input, batteries vastly oversized, or indeed undersized!

If you want to direct email me at chris@offgridsystems.co.uk which will get me at the Off Grid part of our compay. If you can provide the battery type and size too, then I could run through the design for you.

Incidentally solar trackers in this country only provide a small margin over a south facing system. They usually only get used for eco ornaments over here. In soutern Europe, they are perfect and will indeed provide the quoted 40% extra annual power.

Hi - we have just installed a new 4kw PV system with 16 Seraphim panels mounted on a free standing frame which moves to track the sun. We hope that this will prove to be about 30-40% more efficient than a static one. However we are experiencing some teething problems. We have an inverter (Mastervolt Dakar Sine 24/5000) which is located about 15 meters from the array, adjacent to the battery bank of 12 gel batteries & using 2 x Victron Energy Blue Solar charge controllers mppt 150. The system is not charging the batteries and is working less efficiently than our old 2kw system! I am worried that the distance from panels to Inverter may be one of the reasons we have this problem. We can relocate the inverter and battery bank etc but obviuosly this will involve some cost so before doing so we wanted to know if this would help to resolve the problem.

We have lived off grid for almost 2 years so are well organised to minimise our daily electric usage.

Any advice would be greatly approciated as I am a novice and being off grid, it is essential that ths system fiunctions to maximum capability.

The chap who has supplied this doesn't seem to have as much iunderstanding of how the system should/could work as we first thought so a second opinion is needed.

It seems that Tesco Renewable Energy simply had a company called Enact Energy to run the contract. We were contacted by them when they set up to act as an installer some years back. It all felt wrong that an outside company were using Tesco as a front, so we never proceeded. I did not realise they'd ceased trading.

You have a couple of options.. 1) You should have had a warranty from REIGA warranting the product, possibly for 5 years which is quite standard. Conact them first.

2) You may have to bite the bullet and contact a local solar installer to come and deal with the problem. They will do the interface with Deihl and replace the inverter when the warranty replacement arrives. Ask the installer what they charge for this service first, we do this quite often for £100 in the local area. Its an easy job! Some manufacturers like SMA, Fronius, Mastervolt and Solar Edge pay the installer for doing this work so the end user does not incur a cost. I am unsure if Diehl will offer this option though.

Help! My Diehl 3800 S invertor appears to have stopped outputting after 3 years and 4 months of good service which generated 10,351KWH. Whilst it appears to have a 10 year warranty, my problem is that Tesco Renewable Energy has gone bust, as have the organisers of their scheme - Enact Renewables - and the installer BGC Renewables. I have tried to contact Diehl and have submitted a service request on the web but they want me to provide AC and DC voltage readings, which I am not happy about doing myself.

Looking at the error log, thedays leading up to the probem just showed normal startup/shutdown codes E402 and E403. It died with E403 at 15.23 on 21.03.15, 2.5 hours before the typical times of previous days. When I started invesigating on 25.03.15 it recorded E401 code. If I start it up and wait a while, I get an error code on the display of 257 - this is not recorded in the log.

Any ideas on how to fix or who to engage to assist would be appreciated.

You will have had a 3.6kw inverter installed for a couple of reasons.. 1) Your local District Network Operator (ie Western Power, SSE, etc) will not want your system to export more than 3.68kW without special permission, and 2) Most of the time your inverter is generation far less that 3.6kW. The inverter size has to be matched as close as possible to your array size to keep losses low and efficiences high in the system. If you had a 4kw inverter installed, it would perform power conversion for low light days would be worse than you get now.

I have a query regarding my inverter I have a 3.65kwp array of panels but I have a 3.6 KW Inverter is this of a sufficient size or should I have had a 4.0Kw one fitted, I often exceed 3.65Kwp and wonder if my system is safe

Having the inverter in the loft is quite common, especially when space is limited in the house or the panel DC cable run is quite a distance. Though not the best location, it sometimes really is the only solution!

There are a couple of options for checking the power being generated by your system at any time. The cheapest will be the Solo power monitor which you can fit yourself, but does need your FiT meter to have a pulse count LED light that pulses every 100th Kw. If your FiT meter has a flashing light when generating, the Solo will be OK for you. At around £125 is a good buy, especially as you do not need an electrician to install it.

Along the same lines is the Wattson Energy Monitor. We have installed a number of these devices, and found the readout inaccurate and difficult to interpret for some customers. It has a quirky design that could really do with improvement, but I know there is a following of people that love it. As mentioned above though, my issue as been the incorrect power measurement. These can be purchased for sub £100 and you can probably install it yourself.

It may be worth contacting your installer too, as quite a few inverters have an optional wireless display that can installed for £150 or so.

Regarding the timer setup for the summer. You might want to look at the ImmerSun or other similar units on the market right now

Sorry I'd not seen your post earlier, and you may have had a response by now.

This problem has been occurring more and more this year where a number of people on the same substation have had a PV system installed. During sunny weather, the grid voltage will be pushed up by the PV systems all working hard at the same time.

Depending on the inverter type you have installed, the cut off voltage may be 253v or 264v... You need to get the inverter reprogrammed to 264v if the lower, otherwise you will have this problem every summer and lose valuable FiT payments.

Without seeing the damage its hard to tell. As the SB3600TL is only wired by the installer to a power plug on the outside of the inverter, it suggests a faulty connection inside. If the cable to the inverter is damaged, then it could be a faulty connection to the plug.

Any which way, your installer will be able to resolve as SMA have a really good returns policy and can get a service replacement inverter out to your installer with a day or so.

Hi Chris and all, four days ago my SMA sunny boy 3600TL inverter went into
a fault, red light on with message in Germany on the front panel I thick it said
Check fuse. My 4Kw system has only been in about 2 Months the inverter is on
the wall in the garage the 16 panels are Hyundai 250MG. On Monday I got the installer
to check the fault out, he found the main cable to the inverter had got very hot
on the live and neutral wire and the terminal block had broken inside the
inverter. The electrician is looking into new block or new unit from his supplier.
Have you heard of this one before or any ideas what course the fault? (Grid
power or faulty unit etc). Regards Andy.

We also have a Platinum 3800s inverter which keeps dropping out. Installer thinks it is power cuts but our pc's, clocks, etc remain on. This is the second system that we have had - the first installer could not get their system to work (Aug 2011) and eventually removed everything and the new system installed October 2011. It appeared to work fine first of all but was only producing half the expected amount of energy. It is only in the last few days (now that I am retired) that I have noticed flashing lights or sometimes none at all and find it is switching off during the sunniest part of the day! Compared to the original chinese inverter this German made inverter was supposed to be a quality inverter! PV for us has been an expensive lesson in money and grief.

Similar to Bob who posted a comment on 4th May 2011 we have exactly the same problem. Our Diehl inverter switches itself off and registers fault code 201, sometimes up to 13 times a day, usually at peak producing times although not always. We have had our electricity supply monitored for a week by Western Power and they confirm that there is no problem with the supply voltage in terms of fluctuation. Has anyone else had a similar problem with this inverter and, if so, did they manage to resolve it.

This arrangement will not work effectively with the SB2000HF as this inverter is only designed to work with all the modules facing the same direction. It has one Maximum Power Point Tracker (MPPT) input.

MPPT inputs are discrete inputs and some inverters have a number of them. Each of these inputs will be able to get the best out of each array facing different directions.

If modules facing different directions are connected together on a single MPPT input inverter, the shaded array will drag the sunny array output down and you will get mediocre performance no matter what the weather.

Some inverters have a number of input connectors, this does not mean they have more than one MPPT input, as inside the inverter, all these connectors simply connect to the same point. Check the spec sheet to make sure.

Unfortunately, in small inverters (circa 2kW), the choice of multi MPPT input inverters are limited. Until recently we used the Steca 2010+, as this 2kW inverter has 2 MPPT inputs. However in the last year or so we have gone over to using Enecsys micro inverters as they offer a simple robust solution where every panel can face any direction without affecting the others. It also removes the need for having a big inverter box inside the house, and has some great online monitoring. For systems up to 2 kwp the install cost is around the same as having a standard inverter.

There are a couple of different 3kW sunny boy inverters, but assuming you have to the original style with a 2 line text display, as they are quite cheap to buy right now, then 220v is too low a voltage to start the inverter.

Its possible your installer has wired the system in 2 strings, or 2 banks, and connected them in parallel. Unfortunately, with a system of this size and voltage, the inverter will be incompatible on the low end voltage using 2 strings in dull weather, but if connected as one string, the voltage will be too high in sunny weather and show an over voltage warning.

More recent inverters have a wider voltage range, and I suspect a simple inverter change to a Sunny Boy SB3000HF which has a wider voltage range. There are alternatives such as the Kostal Pico 3.6, which has a really wide input range.

Give your installer a call and discuss the problem, they should come out and change the inverter to something compatible. If they are busy, its easy to have miscalculated the voltages, or something got forgotten.

Message: Hi, I have recently had solar pv installed, a 3kw syatem with a 3kw sunny boy inverter. On sunny days the system appears to work as it should but on bright days with light cloud cover the inverter will not connect. The D.C. voltage is shown as 220v but the current as 0.0A. The panels are south facing at a 45deg incline. Neighbours who have the same system fitted regularly produce 150w/h in identical conditions. Could you comment on weather the inverter is at fault or perhaps the d.c. wiring could be too small or any other observations. kind Regards Dave .

To be honest I'm thankful of only really come across and heard about SMA inverters! There's an obvious reason why they are stocked and used by installers. I've had one for just over two years now and I've had absolutely no issues with it.

In regards to the previous comment. I've thought about building a box around it. I'm sure if you follow the guidelines in the handbook then there really shouldn't be a problem.

Hi - I am interested in your comment about placing an inverter in a "large cupboard". We recently installed an inverter in our small conversion, in the living area, thinking we would be able to build a cupboard round it. When the electrician commissioned it recently he advised against this on the grounds that it could overheat and catch fire. The instruction booklet (it's a Sunny Boy) gives a diagram for distances one should allow between the inverter and other objects. If we follow this and build the cupboard at the required distance, and have louvered doors on the cupboard, would you think this would be adequate from a safety point of view? The system is designed for a 3.6 kw output. Thank you - any advice gratefully received!

Hi, I have a 3 sided roof, on a semi detached house. the back roof faces W the front roof E and the side S. It is not affected by shade from the chimney or anything else, we have been visited by 3 companies, one of whom says that we will need micro inverters or stringers, the other company says that we will need 3 inverters in the attic, and the last company says that we do not need more than one inverter for the whole lot.The approx size of panels work out in total to 3.71kw. Could you please advise on the above. Many thanks.

I am trying to find a 700-750w inverter (grid tied) to run 3No 240w panels. Can anyone recommend anything? Also can anyone tell me how to access a database of G83/1 approved equipment? With access to such a database I could more easily search for a suitable inverter.

There are a large amount of inverters in the market place. All for the UK market have been designed to operate to the G83/1 disconnection standard (up to 3.68kW), and will have different displays and facilities that will be available to go with them.

We have used Aurora in the past and found they are a well respected and built unit. There is also a colour touch screen wireless display available at a reasonable cost. SMA we have found are relatively bomb proof and now install these whenever we can as have never had a failure.

It would be unfair to indicate the inverter failures we have had, as some are due to lightning strike and power surges. On both of these latter occasions, all the other houshold electrics got fried too!

At the moment Fronius have extended their extra 10 year warranty to 20 years for no extra charge and SMA also offer extended warranties, up to 20 years. These will incur an additional cost to your basic PV quote, around £300ish depending on inverter.

The industry, in these early days. have assumed the average life of an inverter will be around 12 years, but this has yet to seen on the current crop of higher performance inverters currently on the market.

Summing up..

1) Go for an established brand of inverter. Others are available which may be just as good, but will be offered as part of a 'budget' package.

2) Decide what you want from the inverter in extras. Do you want a wireless display or facility to upload data to the internet?.. If so, that will limit your choices.

3) All inverter manufacturers we have used all have a standard 5 year warranty, and will be confident they will run for that time. If your looking to have extended warranties, make sure you ask your installer at the time of survey, as this will affect their choice of inverter.

Hi Paul 128. Thanks for your enquiry. It's likely that you will have to replace your inverter once during the lifespan of the feed-in tarif. See below for answer by ElectrAssure who says:

"Reliability of the inverter. Life expectancy of an inverter is around
10 years so choose a manufacturer who is likely to be around long
enough to keep spares for, and repair your inverter. You can purchase
an extended warranty from the manufacturers of all good quality
inverters taking the warranty to 20 years in some cases."

Whether the amount you have been quoted for that warranty really depends on your approach to risk.

It's difficult to talk about costs of replacement when you don't say what size installation you're considering. I'd suggest asking any installers that you get to quote, to tell you how long they expect the inverter to last, and what they would charge to replace it. Then you can make realistic long term calculations, and compare like with like.

Am in the process of getting quotes for solar pv. One company has told me they cost £2,500 to replace and another £1,000. I knocked on a door of someone in my area who have solar installed (by another company) and he also told me they were £2,500 to replace.

So how much do they cost to replace - and when they come to be replaced can you put any inverter into the system.

What is the life expectancy of an inverter and is the inverter cost likely to fall in the years to come.

The company that said the cost would be £2,500 also mentioned a fronius inverter which comes with 5 yr guarantee but if you pay £500 you get a warranty for 20years - is this a good deal?

To find out more about the pros and cons of micro inverters have a look at this blog, and click on the following link to read about the merits of the different types of solar PV panels. And if you've got any further questions, do not hesitate to add another question below the relevant blog.

I have just had a visit from a PT system "salesman" who said, inter alia, that the efficiency of the conventional converter depends on the highest panel output, i.e., if any panel suddenly becomes less than 100% efficent, or, say, an end panel becomes obscured as the sun leaves, the output of ALL the panels will fall correspondingly. To avoid this, he recommended integrated inverters, which are fitted to each individual panel

Have I understood him properly and is this so?

He also said that polycrystaline panels were better in that they were more suited to countries that do not have unbroken sunshine (definitely the UK!), but I read somewhere that Europe had now standardised on monocrystalline

Most solar panels are retrofitted onto the roof, but if you're doing it at the same time as your fitting a new roof, then you could also have an integrated system, or you could use solar tiles. I saw some on Solar Century's stand at Ecobuild this year which are designed to be integrated into slate roofs. I'm sure there will be others available too.

In answer to a question I just asked on Twitter, Cotswold Energy Efficient Centre said: "At our centre we have pv in roof & on roof in slate tile your pv
provider should supply the appropriate in roof kit for slate."

Yours is the first question we've received on this subject, so it's not something I've researched yet. However, I'll try and do something on it soon, so keep an eye on the blog.

Usually the slate roof hooks involve drilling through the tiles and screwing the special slate hooks on top of the tiles through to the rafters, but they can be laid under the slates if you are installing at the same time as you are tiling. If you message me over your e-mail address I can send you some photos of both types.

Hi Chris, I currently have a problem with my pv system which is getting worse as the days get longer. 3.96 Kw system installed last November. Diehl Ako 3800s inverter. During March I noticed that the inverter was switching off during the afternoon. I am monitoring my system using a Wattson meter. Around midday with the sun shining and sun at or near its zenith. The inverter goes into standby for 3 mins. Starts up again and then goes into standby. It does this for 2 to 3 hours when it starts working normally again. The length of time that this failure happens is increasing as the days get longer. The installers changed the inverter but it still happens. I think I have an overvoltage problem. The AC side of the inverter reads 255v as it fails. Drops to 250-253 during standby. Then as the inverter comes out of standby the AC voltage quickly rises to 255v before the inverter shuts down again. Later in the afternoon when the inverter is operating normally the AC voltage fluctates between 255 -253v and about 20 minutes late is reading 252 v. In the morning at 7 am with the inverter generating about 100w the AC is reading 246v. I have contacted the DNO and they have fitted a meter to measure my house voltage over a week with the panel array switched off. I think the inverter is shutting off due to overvoltage. I also think that the inverter itself adds to the voltage. It adds volts proportional to amount of watts it is converting. Therefore it is a combination of high DNO voltage (which might or might not be within the statutory DNO limit of 253 v) plus the additive affect of the inverter causing the inverter to shut down due to the voltage it is limited to. The inverter has a fault code of F201 which is "amplitude limit for feed phase exceeded" For example comparing my March generation with a similar sized system nearby shows that the other system generated 200 Kwhr's more than mine.

I want to install PV cells on a new roof, which will be natural slate. The best way to do this must be to install the clips for the PV frame, as the slates are laid. None of the installers i've contacted seem to have done this as most panels are fixed to an existing roof. Comments please

A good post Chris - you have highlighted two of the questions that cause some confusion.

Reliability of the inverter. Life expectancy of an inverter is around 10 years so choose a manufacturer who is likely to be around long enough to keep spares for, and repair your inverter. You can purchase an extended warranty from the manufacturers of all good quality inverters taking the warranty to 20 years in some cases.

On both the DC side and the AC side the issue that you need to avoid is excessive voltage drop. The simple answer is to oversize the cable. The DC and AC cable runs in a PV installation in a house are almost always going to be less than 10 metres. 10 metres of 4mm PV cable will cause negligible voltage drop on the DC side. On the AC side, use the tables in BS7671 (Wiring Regulations) to calculate the voltage drop and choose the cable size (cross sectional area) appropriately. Any competent electrician could do this for you.

If you correctly size the cables you can generally locate the inverter almost anywhere in the house that is convenient for the user to check the display and for maintenance and somewhere that is cool and dust free. Specified maximum operating temperature for a Sunny Boy is 40 degrees centigrade - check the data sheet.

Micro inverters seem like a great idea. but as someone said above, the inverter is the least reliable part of the system so it doesn't make great sense to me to have more of them and site them on or near the roof.

Regarding the operating voltage of the inverter it is the range of voltages (and current or power) that the inverter can handle and whether they match the output voltage (and current and power) range of the array of panels that is the issue. It's no good having an inverter operating at a low voltage if it can't handle the maximum voltage output of the panel array.

It makes sense to use as much of the electricity that your generate to heat your water, run your washing machine, aircon etc etc. Why? Because you will still be paid the FiT on everything you generate, you will still be paid an extra 3p per unit for the 50% estimated to be exported to the grid, AND you wont't be paying for the electricity you are using. Net benefit to you up to 60 pence per unit!

On the subject of inverters, we intend gowing solar and have heard that "Enecsys" produce microconverters to be fitted to each panel so that low DC voltage is converted to AC rather than going in series to high DC. I understand this is more efficient and is a good safety feature. Does anyone have experience and views on these?

Message: I am seriously considering Solar PV but have concerns about the maintenance costs of a system. The figures look good until you realise that the Inverter has a limited life span (say 10 years?), and the panels only have a five year warranty which does not appear to include the cost of access and fitting. is there an insurance scheme at a reasonable price to cover the installation for the 25 years life span that all the figures for return on investment seem to be based on? I realise that there is an output level guarantee with the panels of 20 or 25 years but it appears that this only applies if the panel is still working! Again I don\'t think that access and fitting are included in this guarantee. The investment potential would be quickly wiped out by a couple of panel failures or early inverter problems. Can anybody offer any solutions?

Regarding the comment by David Callister, isn't that down to the panels rather than the inverter? If they produce voltage at low light levels, then the inverter will (should) convert it to AC.

And the comment by blockhead in December - I've looked at the spec for the inverter I have - Shuco - and that's specced up to 90 degrees. 40 degrees seems very low to me, bearing in mind that semiconductors regularly run at 130 degrees without failing so I can easily believe how the Shuco device I have is adequately specified.

Finally with regard to Chris Rudge's comment about siting, I would be concerned about siting an inverter close to a bed, and somebody's head if it were in an adjacent room. But that's only because I'm wary of electric fields. I have no knowledge of what electric fields there are from a grid-tie inverter. Is any information available anywhere in this regard?

Another issue I am wary of in loft spaces is that once the fan gets running on the inverter it can get clogged up with insulation wool and/or dust. Like most things in life, and the construction industry as a whole, it's all about balance and having courage in your convictions. Wherever you site the inverter, take the correct precautions and be prepared to hold your hands up and react positively if it turns out to be wrong.

I am considering installing 4 Kw Solar PV system and one of the companies that has quoted claims that their inverter (power one inverter) runs at a much lower voltage and will therefore generate electricity much earlier than other systems. I am completely new to this technology, it sounds feasible but I just wondered if I am missing something. Also if anyone has had a particularly bad experience installing solar PV I would be interested to know why?

This solar PV panel is a little bit confusing especially if you are new to hear about it. Solar PV panel produces electricity in the form of Direct current that is why every household needs inverter because mostly household devices and appliances requires AC voltage. And inverter converts DC voltage to AC voltage. Inverters are very cost effective today.

I understand the theory of proximity, but the guy who I rate to fit my solar panels etc is adamant that he will not fit any inverter in the loft space. His logic being that all s/facing lofts get very hot, even in our UK summers(well in excess of 45c.) Bearing in mind that many inverter manufacturers spec. their top end temps to 40c (some Sunnyboys) the warrenty would clearly be breached or at least indefensible if in dispute ... so my bloke thinks anyway. My question is, is he being over cautious or are all the other outfits that have recently quoted me being reckless/not aware of individual unit spec.? Help!

Quite right regarding the mains connection to an inverter. Its always best to over specify the cable size to an inverter, especially for longer runs, ie if its installed in an outbuilding remote from the main incoming power.

Hi Chris and all.. One other thing worth considering when placing an inverter is the power loss and voltage drop/rise on the AC connection. Too long or too small a cable here could lose your power and cause the inverter problems with voltage tolerances, particularly in rural locations.